patch 9.0.0206: redraw flags are not named specifically

Problem:    Redraw flags are not named specifically.
Solution:   Prefix "UPD_" to the flags, for UPDate_screen().
diff --git a/src/if_mzsch.c b/src/if_mzsch.c
index 2c0f39c..0c100fe 100644
--- a/src/if_mzsch.c
+++ b/src/if_mzsch.c
@@ -1631,7 +1631,7 @@
 
     // may be use do_cmdline_cmd?
     do_cmdline(BYTE_STRING_VALUE(cmd), NULL, NULL, DOCMD_NOWAIT|DOCMD_VERBOSE);
-    update_screen(VALID);
+    update_screen(UPD_VALID);
 
     MZ_GC_UNREG();
     raise_if_error();
@@ -1836,7 +1836,7 @@
     MZ_GC_UNREG();
     do_set(command, scope);
     vim_free(command);
-    update_screen(NOT_VALID);
+    update_screen(UPD_NOT_VALID);
     curbuf = save_curb;
     curwin = save_curw;
     raise_if_error();
@@ -2106,7 +2106,7 @@
     win->win->w_cursor.lnum = lnum;
     win->win->w_cursor.col = col;
     win->win->w_set_curswant = TRUE;
-    update_screen(VALID);
+    update_screen(UPD_VALID);
 
     raise_if_error();
     return scheme_void;
@@ -2781,7 +2781,7 @@
 	}
 
 	curbuf = savebuf;
-	update_screen(VALID);
+	update_screen(UPD_VALID);
 
 	MZ_GC_UNREG();
 	raise_if_error();
@@ -2841,7 +2841,7 @@
 	free_array(array);
 	MZ_GC_UNREG();
 	curbuf = savebuf;
-	update_screen(VALID);
+	update_screen(UPD_VALID);
     }
 
     MZ_GC_UNREG();